Randall RG-120 No Tremolo (& More) Help

[Helmholtz]

The MPS 6522 and the BC560C show negative V in the specs, but I have positive V from the C node at this part of the circuit. I am confused by this.
Also I have a good used MPS 6533 (spec below) with higher V ratings and would like to know if I can use it to replace the 6522?

Pnp needs collector to be negative wrt emitter. Same thing happens when collector is less positive than emitter.

MPS 6533 might work but has less current gain (Hfe), so less available current for the light source.

[misterc57]

I installed the MPS 6533 and also replaced R79 (thinking it may bump up the B and A node V, but it did not.

Reading the following on Q21 now

E 36.45 V
B 35.7 V
C 3.4 V

Collector is pulsing but only when the speed knob is above 7

E to B V is .6 V

Still NOT hearing any tremolo effect.

BC560C is not so easy to find at normal prices. I see some kits (which I would rather order) for the same price of a few BC560C that I can order from Amazon and have delivered within 2 days.

None have the BC506C but they include other values (see below), would any of these work such as the BC557?

Thank you

[Helmholtz]

BC557 should work.

Do you have the trem depth fully on?
Actually transistor voltages don't look too bad now, but higher Hfe should increase trem intensity.

[misterc57]

Do you have the trem depth fully on?

I guess I did not because it is now working fine. YAY!!! Thank you

Now the reverb...

Tank is good with proper resistance at input and output. I hear no reverb effect.

Not sure where to begin. Thank you

[nosaj]

slap the top of the amp real hard do you hear a crashing of the reverb?
nosaj

[misterc57]

slap the top of the amp real hard do you hear a crashing of the reverb?
nosaj

Chassis and tank are out of the cabinet and on the bench. No crashing sounds when moving banging the tank.

[misterc57]

If anyone has a more legible copy of the schematic that would help me as it is really hard to read.

[nosaj]

Do you have a scope? or a signal tracer? any chance reverb cables are reversed?
nosaj

[Helmholtz]

Problem seems to be on the recovery side.
As always check cables, contacts and DC voltages first.

[misterc57]

So the reverb output, recovery side, is the upper portion of the schematic with Q18 and Q19, right?

I can hear a signal at the input side of the tank but nothing at the output side of the tank.

[misterc57]

Q18
E 1.4 V
B .09 mV
C 15.6 V

Q19
E 20.7 V
B 15.5 V
C 16 v

[misterc57]

Do you have a scope? or a signal tracer? any chance reverb cables are reversed?
nosaj

Yes on test equipment. Tried cables swapped.

[Helmholtz]

Q18
E 1.4 V
B .09 mV
C 15.6 V

Q19
E 20.7 V
B 15.5 V
C 16 v

Voltages are somewhat off from schematic but should be ok.
Schematic identifies Q18 as Jfet, so S,G,D instead of E,B,C.

Are the reverb springs intact?

For further testing you will need to inject a signal to the recovery amp.

[nosaj]

So the reverb output, recovery side, is the upper portion of the schematic with Q18 and Q19, right?

I can hear a signal at the input side of the tank but nothing at the output side of the tank.

By this statement it says to me something is wrong with the tank maybe something wrong with one of the transducers.
If you have a test tank I'd try it.
nosaj

[misterc57]

Tried a different tank, still not working. Both tanks test good on resistance. about 27 ohms at input and 240 ohms at output..

I inject a signal at the output of the tank and it did pass through to the speaker.

Weird???